When the number of data receiving terminals increases in the conventional client-server data distribution system, a distribution load occurs correspondingly in the distribution server. Therefore, a large system requires the reinforcement of the distribution servers where access concentrates and network infrastructure, thereby causing the problem of a higher distribution cost.
With the background above, the distribution performed by applying the P2P technology has recently been highly regarded. As a P2P streaming distribution method, there is a method in which a terminal that has received data relays the received data to another terminal, the data is sequentially relay-distributed from terminal to terminal, thereby realizing a distribution on a large scale and generating a moderate of no increase of the distribution load of the distribution server in response to an increasing number of terminals.
A P2P distribution can be regarded as a data distribution on a logic network (overlay network) formed by a logic link between terminals.
On the other hand, grasping and managing the information about terminals configuring the P2P network in the P2P data distribution is very important from the viewpoints of security, accounting in a commercial service, etc. The terminals can be managed in the system of providing a dedicated server (terminal management server) for centrally managing them. However, in a large system having a large number of terminals, the information access concentrates on the terminal management server, which is the bottleneck and causes degraded scalability.
A common system for reducing the load of the management of the terminal information above is to group the terminals and provide the terminal management server for each group, and manage the information by the group. When the number of terminal increases, the number of terminals in a group can be suppressed by increasing the number of groups. Therefore, the terminal management server of each group can reduce the growth of a management load.
In this case, it is desired that the relay transfer of data can be performed between the terminals in the same group because the effect of the communication traffic between the terminals on a physical network can be reduced when the relay transfer is performed between the same group with a physical network configuration designed to group the terminals close to one another on the network.
The patent document 1 discloses the conventional technology of grouping terminals in a P2P relay distribution and establishing a distribution path in a group.
The conventional technology is data relay type contents distribution technology for grouping terminals for relay transferring data, and dispersing the load of a server, thereby improving the band use efficiency of each terminal including the server.
In the grouping process, one group is formed by collecting terminals close to one another in data transfer band, and generating a path of a daisy chain in the group with a terminal having a wide band determined as an upstream terminal. Thus, data is distributed.
When a terminal on a distribution path deviates from the relay distribution in a daisy chain due to a fault etc., a terminal upstream to the faulty terminal detects the fault and amends the path to skip the deviating terminal and transfer the data to the downstream terminals, thereby maintaining the distribution.
In the grouping process by another conventional technology disclosed in the following patent document 2, relay terminals are arranged in the descending order from the terminal having the widest transfer bandwidth in the contents distribution similar to the distribution by the above-mentioned conventional technology, the groups are assigned from the first group to the Nth group, and then inversely assigned from the Nth group to the first group, and the processes are repeated, thereby configuring the groups to average the performance and the numbers of the member terminals in each group.
Also in this system, the distribution path in a group is a daisy chain, and the relay can be maintained by skipping a faulty terminal when a fault occurs, thereby easily amending the path.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2004-3182741
[Patent Document 2] Japanese Laid-open Patent Publication No. 2004-199578
The two above-mentioned conventional technologies (patent documents 1 and 2) are terminal management systems for improving the scalability by grouping and managing terminals. The grouping processes in the conventional technologies are optimized to obtain an effect of shortening the download time in the download and distribution system in which the relay distribution in a group is performed through one relay path in a daisy chain. When a relay terminal is stopped, the stopped terminal is skipped, thereby successfully continuing the distribution.
On the other hand, the data distribution speed is constant in many cases in the streaming distribution in which the distribution efficiency is attained by increasing the number of broadcast terminals, not by shortening the distribution time.
Therefore, the distribution path in a group is not a daisy chain, but a tree-shaped or a mesh-shaped path, and a terminal having a wide transfer bandwidth simultaneously relay-transfers data to a plurality of terminals.
FIG. 36 illustrates an example of a distribution path for one group as a part of the P2P distribution system in which each terminal is connected through a tree-shaped distribution path and data is relay-distributed through the path. When terminals are grouped in the streaming distribution through the above-mentioned distribution path, there occurs a problem in grouping the terminals with the above-mentioned conventional technologies applied as is.
In FIG. 36, each terminal is illustrated as a circle, and the status of each terminal is represented by the numerals accompanying the circles indicating the “band in use/possessed band”. For example, the terminal a has the possessed band (corresponding to the band/bandwidth available to and possessed by terminal a) of 2B which is exactly double the bandwidth of distributed data B, and uses 2B because the received distributed data is copied inside and relayed to the terminals b and c. Therefore, the terminal is indicated by [2B/2B].
In FIG. 36, it is apparent that all terminals have used the possessed bands
In the above-mentioned conventional technologies, a group is configured by terminals having possessed bands close to one another, or by terminals such that the possessed bands of each group are assigned evenly. If a tree-shaped or mesh-shaped path is designed in a group, there is no sufficient room for the transfer band in the group as illustrated in FIG. 36.
At this time, if a terminal (terminal a illustrated in FIG. 36) relaying two or more terminals goes down for any reason, one of the terminals b and c immediately below the terminal M that has lost the distribution destination and has therefore reduced bandwidth in use can receive data by maintaining the connection, but the other has no terminal capable of transferring data in the group, loses the distribution source, and cannot continue to receive data.
In this case, the distribution path can be amended by a search for a terminal that can be a distribution source in another group. However, amending a connection path using labor and time in a communication sequence with another group after detecting a path disconnection (reception stop) state is not desired because it stops video and audio in the real time streaming distribution.
As described above, there is the problem with the conventional technologies that a path cannot be repaired in the group.